We will develop reagents and methods to assign genes to specific chromosomal locations in both a germinal and a highly differentiated somatic nucleus in the ciliated protozoan Tetrahymena thermophila. For mapping in the germinal nucleus, we will develop both nullisomic (missing both copies of one of the five chromosomes) and deletion strains. Cells with these genotypes will be viable, because they will have normal, nondeficient, somatic nuclei. These strains will be mated to strains containing known mutations, to efficiently construct a genetic map of this organism. They will also be used to isolate new mutations in specific parts of the genome. Genetic linkage in the differentiated somatic nucleus will be identified by isolating newly induced mutations that undergo phenotypic assortment with known genes. The somatically linked genes will then be mapped in the germ line using conventional and deficiency crosses, to allow a comparison of germinal and somatic genetic organization.